This invention belongs to the field of agricultural chemistry, and provides to the art a new method of controlling aquatic weeds and algae. The safe control of aquatic weeds and algae has become more and more important. Such weeds and algae clog water-ways, plug up water-handling equipment, are often aesthetically unacceptable, and can become so lush that even fish populations are injured. In addition, many types of algae are toxic to mammals. Therefore, herbicides effective against aquatic weeds and algae are in demand and research on the subject has been going forward with vigor.
The compounds used in the method of this invention kill the plants slowly, so that their decomposition does not deplete oxygen in the treated body of water, and are quite safe to fish, phytoplankton and zooplankton.
Despite the great amount of research which has been performed in the field of agricultural chemistry, active compounds closely related to the compounds of the present invention have not been previously discovered. The polyhalopyridones, which have two or more chlorine atoms as well as other alkyl and halo substituents on the pyridine ring, are known herbicides, but are obviously quite distinct from the present invention.
The organic chemical art has explored the pyridones rather extensively. For example, Ishibe et al., J. Am. Chem. Soc. 95, 3396-3397 (1973), disclosed a rearrangement of 3,5-diphenyl-1,2,6-trimethyl-4(1H)-pyridone. Such compounds, however, are not herbicides. Leonard et al., J. Am. Chem. Soc. 77, 1852-1855 (1955), taught the synthesis of 3,5-dibenzyl-1-methyl-4(1H)-pyridones, which compounds also have no herbicidal activity. The same principal author also disclosed 3,5-di(substituted-benzylidene)tetrahydro-4-pyridones, J. Am. Chem. Soc. 79, 156-160 (1957).
Light et al., J. Org. Chem. 25, 538-546 (1960), taught a number of 4-pyridone compounds including 2,6-diphenyl-1-methyl-4(1H)-pyridone, and related compounds bearing phenyl-ring substituents, none of which are herbicidally active.
An interesting recent article was published by El-Kholy et al. in J. Hetero. Chem. 10, 665-667 (published Sept. 7, 1973). El-Kholy described a synthesis of 3,5-diphenyl-1-methyl-4(1H)-pyridone and related compounds by the reaction with methylamine of the sodium salt of 1,5-dihydroxy-2,4-diphenyl-1,4-pentadien-3-one.
A counterpart of the parent application, Ser. No. 591,661, has been patented as Belgian Pat. No. 832,702 (1976).
Articles and reports reporting the herbicidal use of compounds of this invention include the following:
Anonymous, Technical Report on Fluridone, Lilly Research Laboratories, Indianapolis, Indiana.
Berard and Rainey, Weed Sci. Soc. of Am. Abstracts 28, p. 13 (1977);
Parka, Fluridone: A New Herbicide for Use in Aquatic Weed Control Systems, Proceedings of the European Weed Research Society, Amsterdam, September 1978.
Waldrep and Taylor, J. Agric. Food Chem. 24, 1250-51 (1976);
Waldrep and Taylor, Weed Sci. Soc. of Am. Abstracts 266, p. 109 (1977);
Webster, Proc. Southern Weed Sci. Soc. 30, 103-12 (1977);
Wills, Proc. Southern Weed Sci. Soc. 30, 113-18 (1977).